The invention relates to a camshaft adjusting device and to a central valve for a camshaft adjusting device.
Camshaft adjusting devices are generally used in valve trains of internal combustion engines to change the valve opening and closing times, which can improve the consumption values for the internal combustion engine and the performance characteristics in general.
An embodiment of the camshaft adjusting device that has proven effective in practice has a vane cell adjuster with a stator and a rotor that define an annular space divided by projections and vanes into several work chambers. The work chambers can be loaded selectively with a pressurized medium that is fed in a pressurized medium circuit via a pressurized medium pump from a pressurized medium reservoir into the work chambers on one side of the vanes of the rotor and is fed back into the pressurized medium reservoir from the work chambers on the other side of the vanes. The control of the pressurized medium flow and thus the adjustment movement of the camshaft adjusting device is realized, e.g., by means of a central valve with a complex structure of flow openings and control edges and a valve body that is displaceable in the central valve and closes or opens the flow openings as a function of its position. The valve body itself is spring-mounted relative to the central valve and is shifted against the spring force by means of a contacting piston of an actuator for adjusting the rotational angle of the rotor relative to the stator. The rotor is usually connected to the camshaft, while the stator is driven, e.g., by means of a chain or a belt, by a crankshaft of the internal combustion engine so that the rotational angle of the camshaft to the crankshaft is also adjusted by adjusting the rotor relative to the stator.
The camshaft adjusting device thus comprises a plurality of components with a complex structure of pressurized medium channels, openings, and control edges, which include, in particular, the central valve, the valve body, and the rotor. Due to the complex shaping and due to cost reasons, certain components, e.g., parts of the central valve, are made from plastic.
As the pressurized medium, preferably hydraulic oil is used that is heated to high temperatures up to 100 degrees when the internal combustion engine is running and is continuously cooled by the coolant circuit of the internal combustion engine. The pressurized medium is pressurized at least when the camshaft adjusting device is actuated with unavoidable pressure spikes that can lead, in extreme cases, to damage to the plastic parts, especially in connection with the higher temperatures and a resulting negative change to the strength properties of the plastic.